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Chapter 5. Excitable Tissue: Muscle

The action potential of skeletal muscle

A. has a prolonged plateau phase.

B. spreads inward to all parts of the muscle via the T tubules.

C. causes the immediate uptake of Ca2+ into the lateral sacs of the sarcoplasmic reticulum.

D. is longer than the action potential of cardiac muscle.

E. is not essential for contraction.

The functions of tropomyosin in skeletal muscle include

A. sliding on actin to produce shortening.

B. releasing Ca2+ after initiation of contraction.

C. binding to myosin during contraction.

D. acting as a “relaxing protein” at rest by covering up the sites where myosin binds to actin.

E. generating ATP, which it passes to the contractile mechanism.

The cross-bridges of the sarcomere in skeletal muscle are made up of

A. actin.

B. myosin.

C. troponin.

D. tropomyosin.

E. myelin.

The contractile response in skeletal muscle

A. starts after the action potential is over.

B. does not last as long as the action potential.

C. produces more tension when the muscle contracts isometrically than when the muscle contracts isotonically.

D. produces more work when the muscle contracts isometrically than when the muscle contracts isotonically.

E. decreases in magnitude with repeated stimulation.

Gap junctions

A. are absent in cardiac muscle.

B. are present but of little functional importance in cardiac muscle.

C. are present and provide the pathway for rapid spread of excitation from one cardiac muscle fiber to another.

D. are absent in smooth muscle.

E. connect the sarcotubular system to individual skeletal muscle cells.

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